Process for electrodepositing uranium dioxide



Jan. 8, 1952 KAHN 2,581,863

PROCESS FOR ELECTRODEPOSITING URANIUM DIOXIDE Filed March 24. 1945 IN V EN TOR.

milion Hahn BY A T TOENE Y Patented Jan. 8, 1952 #11 .iJNl-TED STATES ATENT] OFFICE PROCESS FOR ELECTRODEPOSITING V URANIUM DIOXIDE Milton Kahn, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application March .24, 1945, Serial No. 584,686

3 Claims. (01. 204-96 This invention relates to the electrolytic depoof uranium for use in various other instruments and procedures.

It is often necessary to prepare layers of metal or metal compounds for work in which only thin, uniform films can be employed. One such procedure is for the isotopic analysis of metal, such as uranium, as described in the co-pending United States Application Serial Number 536,440 filed May 19, 1944, by Segre and Kennedy, now abandoned. In that method of analyzing polyisotopic uranium, independent measures of mass of sample, and of slow-neutron-produced fission of the sample are required. The last two of these measurements may be made utilizing a target comprising a thin layer of uranous-uranic oxide (U308) on a platinum foil backing. In preparing these targets of uranium for isotopic analysis, it is necessary to prepare the uranium sample as a suitable composition (preferably as substantially pure uranous-uranic oxide) in the form of the film of such thickness that very little alpha particle absorption occurs within the film. A film thickness corresponding to approximately four hundred micrograms of uranium per square centimeter is taken to be about the maximum allow able.

In the prior art process of preparing these target films, chemical methods have generally been employed but considerable difiiculty has been encountered in obtaining uniform, thin layers of the desired thickness thereby.

It is an object of this invention to provide methods for improving the Kennedy and Segre method of isotopic analysis, by simplifying the preparation of suitable metal compound films and by eliminating the attendant failures in the prio art methods of film preparation.

It is the further object of this invention to prepare suitable uniform, thin films of metal compounds for use in various procedures by electrodeposition of oxides or hydroxides of uranium.

It is another object of this invention to provide an improved process for preparing a suitably thin film of polyisotopic uranium, whereby eter ne I It is still another object of this invention to provide an improved process of preparing a suitably thin film of purified uranium, as uranousuranic oxide, whereby the isotopic composition of the uranium may be determined.

Still another object of the invention is to provide aprocess of electrodepositing a sample of uranium in the form of a film whereby the isotopic composition of the uranium may be deter-. mined.

A still further object of the invention is to provide a process for electrodepositing a sample of uranium as a film of uranium dioxide and ignit-i ing the uranium dioxide to uranous-uranic oxide, whereby the isotopic composition of the uranium may be determined.

. will appear from the following detailed descripuranium dioxide on the cathode.

tion including claims and drawings.

In general the present process is directed to the electrolysis of an aqueous alkaline solution of a soluble ionizing oxycompound of uranium so that the +6 metal is reduced at the cathode to the +4 or +3 state and precipitates as the oxide or hydroxide. For example the electrolysis of an alkali metal hydroxide solution of uranyl nitrate (with or without alkali metal carbonate) deposits may be converted to uranous-uranic oxide by igniting.

By this process oxide or hydroxide films of the order of four hundred micrograms of metal per square centimeter can be prepared. It is preent invention will appear from the following detailed description taken in conjunction with the drawing forming part of this specification in which drawing Figure 1 is a vertical section of the electrodeposition cell, Figure 2 is a horizontal sectional ,view taken on the line 22 of Figure 1v showing details of the electrodeposition cell, and Figure 3 shows a conventionalized perspective view with partsout of scale and proportion for clarity of the finishe d target. I I

This coating His placed on a larger and thicker platinum disk,

12, which is about 0.010 inch in thickness and about two inches in diameter and which is cut so that a tab 13 extends out from the disk and makes connection with the wire it to which a negative potential may be applied. in turn, the platinum disk I2 is placed on the ground glass plate I5 which serves as a supporting base for the electrodeposition cell It. The glass cylinder [6, which is provided with a suitable number (preferably four) of appendant glass hooks H and has an outside diameter which is a little less than one and one-half inches, in concentrically placed upon the platinum disk ii and is secured to this position by passing a band 22 of rubber or the like alternating under the hooks 48 which are arranged in the glass plate 15, as indicated on the drawings, and over the hooks ll of the glass cylinder IS. A liquid-tight seal is formed at the junction of glass cylinder and platinum disk Ii by forming a fillet is of beeswax or the like around the outside of the junction. This is accomplished by applying, with a small brush, molten beeswax to the junction, the beeswax being well above its melting point in order to assure a good seal.

'The anode 20 comprises an approximately nine inch length of platinum wire of one-sixteenth diameter of which about six and one-half inches of the length are wound in a spiral leav ing about two and one-half inches of straight wire for connection to a stirrer. The platinum anode is fastened in the chuck of the small variable speed'electric stirrer, not shown, and the position of this stirrer is adjusted so that the spiral anode dips about :half way down into the electrodeposition cell It). The anode is clea trically connected so that it is at a potential positive to that of conductor 14 and .is ordinarily grounded. The electrodeposition cell ill is now completely assembled and is ready for use.

in the case where uranium is to be deposited as uranium dioxide on the platinum disk H, about ten milliliters of an alkaline carbonate solution (made by adding four grams of potassium carbonate to two hundred milliliters of 0.15 M potassium hydroxide solution thus producing a solution in which the concentration of the carbonate ions and the hydroxyl ions are approx imately equal) and about five milliliters of substantially pure uranyl nitrate solution which has been prepared from the uranium sample ,to'

grams of uranium per square centimeter is formed when the uranium is deposited. It will thus be apparent that the concentration of carbonate and hydroxide ions will be from about 200 times to 3,000 times the concentration of the .uranyl ions. As previously mentioned, such a film is of about the maximum allowable thickness for analytical purposes. A potential of about seven volts is applied to the electrodeposition cell l0, whereby a current of about fifty milliamperes having a current density of about 0.6 ampere per sq. decimeter flows through the cell. At the same time the variable speed electric stirrer (not shown), is turned on, whereby the platinum wire anode 2b is causedrto rotate at a suitable speed. The action of the applied potential is to cause the uranium as uranyl ion, UO2++, to migrate to the platinum disk H and be reduced toja uranous ion, U which combines with neighboring hydroxylions and precipitates as uranium dioxide or, more precisely, as the hydrated dioxide U022H2O or the hydroxide U(OI-I)4 on the platinum disk H.

Current is allowed to flow through the electrodeposition cell It] until the uranium in the cell is substantially completely deposited in a layer H on the platinum disk I I. This is accomplished in about ninety minutes. After the current is turned off the solution is poured out of the cell and the cell is rinsed with water. The platinum disk I i is then detached from the cell and again washed with water. The disk is next ignited in an oxidizing flame for about one minute, whereby any beeswax on the disk is burned oil and the exceptionally pure uranium dioxide deposit 22 is quantitatively converted to uranous uranic oxide, 'UsOa.

The platinum disk ll, accordingly, is covered with a thin uniform film of U308 and is ready for the isotopic analysis in accordance with the previously mentioned Segre-Kennedy procedure. This method includes weighing the target, then supporting the target upon a copper base plate and subjecting it to alpha activity and fission activity measurements, whereby both the alpha activity of the U308 and the fission activity under slow neutron bombardment :of. the U388 are :determined.

A further example of plating uranium dioxide is to electrolyze in the cell of Figure l, fifteen c. c. of an aqueous solution containing about "780 micrograms of uranium as uranyl nitrate and about 0.21 gram of potassium hydroxide which provides a hydroxide ion concentration of about 1200 times that-of the uranyl ion concentration. A potential of about three volts is .applied =:to the cell wherebya current of about one hundred milliamperes (current density of thirteen milliamperes per square centimeter or 1:3/am-ps. sq. decimeter) flows therethrough. Current :is =allowed to flow 'through'the 'cell'until the uranium therein is substantially completely deposited on the platinum disk. This requires about .one hundred and sixty minutes. The plated film is treated as in the precedingexample. "The yield of uranium is checked byweightand by alpha activity and found to be about The film density is about ninety micrograms per square centimeter.

In view of the foregoing, -it-is apparent that there -has been provided an improved method for preparing u-ranlum i-n a pure form as -a thin filmof U308 in-which form-the uranium may'be analyzed for its isotopic composition. *The'prem aration is accomplished by electrodepositing the uranium as uranium dioxide on a backing member, such as a thin platinum disk, and subsequently igniting the uranium dioxide to U303.

The process can be applied to other metals which form soluble higher valence oxycompounds and insoluble lower valence oxides or hydroxides by substituting a corresponding molecular quantity of these metals for the uranium. The ions of such metals should be more susceptible to change in the electrolysis than the anion of the oxycompound and the hydroxl ions should be in large excess over the metal ion at the cathode in order to have the process effective.

The important factor in this type of electrolysis is to keep the ratio of the concentration in the solution of the uranyl ion to the hydroxyl ion very small so that when the reduced ion (+4 or +3 state) is produced, its rate of difiusion from the cathode will be smaller than the rate of diffusion from the aqueous solution to cathode by the hydroxyl ion. This electrolytic process is to be distinguished from the preparation of films of metal compunds by electrophoresis of colloidal suspensions.

While what has been described is at present considered to be preferred embodiments of the invention, it will be understood that various modifications may be made therein. Thus, for example, backing members of noble metals other than platinum, such as gold, palladium or the like, may be used. Also, for example, soluble salts other than the nitrates, as given in the examples, may be used.

The term uranium, as used in the specifications and claims is used generically to refer to this material whether in elemental or combined state except where indicated otherwise by the context. The term oxide as used in the specification and claims is to include the hydrated oxides or hydroxides unless otherwise indicated by the con text.

As many widely different embodiments of this' invention may be made without departing from the spirit and scope thereof, it is to be understood that the applicant does not limit himself to the specific disclosures and embodiments except as defined in the appended claims.

What is claimed is:

1. The process for electrodepositing uranium dioxide which comprises contacting two inert electrodes with a dilute aqueous solution wherein 6 the solute consists essentially of uranyl nitrate and at least one material from the class consisting of potassium carbonate and potassium hydroxide, the amounts of said materials being 5 such that the concentration of the negative ions of said materials is from about 200 times to 3000 times the concentration of the uranyl ion, and passing a direct current through the said solution at a current density of between 0.6 to 10 1.3 amperes per square decimeter for a period of from about 90 to about 160 minutes.

2. The process of claim 1 wherein the molar concentrations of the carbonate ion and the hydroxyl ion are approximately equal, and current is passed through the solution at a potential of 7 volts and a current density of 0.6 ampere per square decimeter for a period of about 90 minutes.

3. The process for electrodepositing uranium dioxide which comprises contacting two inert electrodes with a dilute aqueous solution wherein the solute consists essentially of uranyl nitrate and potassium hydroxide in amounts such that the molar concentration of the hydroxyl ion is about 1200 times that of the uranyl ion,

and passing a direct current through the said solution at a potential of about 3 volts and a current density of about 1.3 amperes per square decimeter for a period of about 160 minutes.

MILTON KAHN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 571,531 Langhans 1. Nov. 17, 1896 1,448,036 Pearson et al Mar. 13, 1923 2,059,053 Stareck Oct. 27, 1936 2,081,121 Stareck May 18, 1937 OTHER REFERENCES 

1. THE PROCESS FOR ELECTRODEPOSITING URANIUM DIOXIDE WHICH COMPRISES CONTACTING TWO INERT ELECTRODES WITH A DILUTE AQUEOUS SOLUTION WHEREIN THE SOLUTE CONSISTS ESSENTIALLY OF URANYL NITRATE AND AT LEAST ONE MATERIAL FROM THE CLASS CONSISTING OF POTASSIUM CARBONATE CARBONATE AND POTASSIUM HYDROXIDE, THE AMOUNTS OF SAID MATERIALS BEING SUCH THAT THE CONCENTRATION OF THE NEGATIVE IONS OF SAID MATERIALS IS FROM ABOUT 200 TIMES TO 3000 TIMES THE CONCENTRATION OF THE URANYL ION, AND PASSING A DIRECT CURRENT THROUGH THE SAID 